The invention relates to a magnetic-tape cassette comprising a housing which comprises two rectangular parallel main walls, between which two reel hubs on which a magnetic tape is wound are arranged so as to be rotatable about axes of rotation which extend substantially perpendicularly to the main walls. Each main wall has openings which are substantially coaxial with the reel hubs and which are bounded by cylindrical centering rims which extend inwardly relative to the main walls and which center the reel hubs inside the housing relative to the openings. A liner foil is positioned against the inner side of each main wall and bears elastically against the turns of magnetic tape and against the axial end of the reel hub.
A magnetic-tape cassette of this type is disclosed in German Offenlegungsschrift No. 2,121,375. Inside the housing of such a cassette the axial ends of the reel hubs are positioned against liner foils which have upwardly inclined supporting edges and bear elastically against the main walls near their two longitudinal sides. During winding and unwinding of the magnetic tape such foils bear against the rolls of tape on the reel hubs in order to preclude tilting of the tape rolls relative to the main walls. In order to achieve this it is important to minimize the friction between the tape edges and the foils. In the area near the reel hubs the foils have a comparatively high elasticity and at this location they can readily be urged towards the main walls. As a result of this elasticity, the reel hubs can also readily move in an axial direction, so that it is not unlikely that the reel hubs are also tilted to a certain extent relative to the main walls.
These movements may give rise to a slightly tilted position of the tape rolls in spite of the supporting action of the foils. Such tape roll tilting during tape transport may result in an irregular movement of the tape inside the housing. In practice, this may lead to problems if during the tape transport inside the housing the tape edges move at irregular distances from the main walls, and cause azimuth errors. These errors result from the magnetic tape being positioned in such a way at the location of the magnetic head that the longitudinal axis of the tape no longer extends perpendicularly to a plane through the air gap of the magnetic head. Such azimuth errors lead to a deterioration in higher-frequency reproduction and are therefore undesirable.
It is to be noted that German Offenlegungsschrift No. 2,327,828, to which U.S. Pat. No. 3,923,272 corresponds, describes a magnetic-tape cassette in which the foil is tensioned to some extent near centering rims on the main walls, by providing an axially projecting inner ring on the reel hub. In this known cassette the thickness of the two main walls is slightly reduced near the centering rims, so that at this location some clearance exists to allow axial movements of the reel hub. Since the thickness of the other parts of each main wall is comparatively large, the axial clearance for the tape roll is comparatively small. This is liable to give rise to jamming of the tape roll. Further, this known magnetic-tape cassette does not have a supporting ring which provides a corrective action.